1. Field of the Invention
The present invention relates to a semiconductor device having a circuit consisted of a thin film transistor (hereinafter, referred to as TFT) in which the peeled off layer peeled off has been pasted and transferred on a base member and a method of manufacturing the semiconductor device. For example, the present invention relates to an electro-optic device that is represented by a liquid crystal module, a light emitting device that is represented by an EL module and an electronic equipment on which such a device is mounted as a part.
It should be noted that in the present specification, the term “semiconductor device” indicates a device in general capable of functioning by utilizing the semiconductor characteristics, and an electro-optic device, a light emitting device, a semiconductor circuit and an electronic equipment are all semiconductor devices.
2. Related Art
In recent years, a technology constituting a thin film transistor (TFT) using a semiconductor thin film (in the range from about a few to a few hundreds nm in thickness) formed on the substrate having an insulating surface has drawn attention. A thin film transistor is widely applied to electronic devices such as an IC, an electro-optic device or the like, and particularly, there is an urgent need to be developed as a switching element for an image display device.
Although as for applications utilizing such an image display device, a variety of applications are expected, particularly, its utilization for portable apparatuses has drawn the attention. At present, although many glass substrates and quartz substrates are utilized, there are defaults of being easily cracked and heavy. Moreover, the glass substrates and quartz substrates are difficult to be made larger in therms of conducting a mass-production, and these are not suitable for that. Therefore, the attempt that a TFT element is formed on a substrate having flexibility, representatively, on a flexible plastic film has been performed.
However, since the heat resistance of a plastic film is low, it cannot help lowering the highest temperature of the process. As a result, at present, a TFT is formed which has not so excellent electric characteristics compared with those formed on the glass substrates. Therefore, a liquid crystal display device and light emitting element having a high performance by utilizing a plastic film have not been realized yet.
If a light emitting device or a liquid crystal display device constituted of an organic light emitting device (OLED) formed on a flexible substrate such as a plastic film can be fabricated, it can be obtained as a thin lightweight device and can be used in a display having a curved surface, a show window, etc. Use of such a device is not limited to use as a portable device, and the range of uses of such a device is markedly wide.
However, substrates made of plastics ordinarily have permeability to water and oxygen, which act to accelerate degradation of the organic light emitting layer. Therefore, light emitting devices using plastic substrates tend to have a shorter life. By considering this problem, a method has been used in which an insulating film of silicon nitride or silicon nitroxide is formed between a plastic substrate and an OLED to prevent mixing of water and oxygen in the organic light emitting layer.
Also, generally speaking, substrates formed of plastic film or the like are not resistant to heat. If the temperature at which an insulating film of silicon nitride or silicon nitroxide is formed on a plastic substrate is excessively high, the substrate deforms easily. If the film forming temperature is excessively low, a reduction in film quality results and it is difficult to effectively limit permeation of water and oxygen. There is also a problem in that when a device formed on a plastic film substrate or the like is driven, heat is locally produced to deform a portion of the substrate or to change the quality thereof.
Further, if the thickness of the insulating film of silicon nitride or silicon nitroxide is increased in order to prevent permeation of water and oxygen, a larger stress is caused in the film and the film cracks easily. If the film thickness is large, the film cracks easily when the substrate is bent. Also, a layer to be debonded may crack when it is bent at the time of separation from the substrate.